X-Message-Number: 2049
Subject: CRYONICS: patient storage
Date: Thu, 01 Apr 1993 17:51:37 -0500
From: "Perry E. Metzger" <>
I've been following the discussion about high temperature patient
storage for a while, and only started thinking about this seriously in
the last day or two after it was obvious that people are talking about
actually building such units soon.
I hope I don't insult anyone by bringing up topics that have already
been hashed out a million times before -- my apologies in advance if I
do.
I have several question, some simple minded, some not. I imagine that
everyone involved has already thought of all these things -- I am more
running on the assumption that you have and that I simply somehow
missed the discussion.
1. a simple-minded question. I was under the impression that you could
buy commercial freezer units that operated at the temperatures in
question. Wouldn't it be simpler and cheaper either to buy such units,
or, if they are too small, to commission a manufacturer of such units
to build extra-large units? Again, I would understand that such a
solution would be dismissed out of hand if such units did not exist,
but my understanding is that they do exist, at least for storing cell
samples. Also, given that people build such units, would they not have
far more experience in what sort of insulation systems are most
efficient for them, since they do this for a living and we are merely
amateurs?
2. Another issue I haven't seen addressed too much is this: precision
of temperature regulation. The systems that have all been mentioned
thus far sound like they would expose patients to relatively large
temperature swings compared to the "stay at the boiling point of LN2
forever plus or minus a few tenths" system that we have now. Does
anyone know if such swings might in and of themselves induce damage in
the patients? If no one knows, isn't this something to do experiments
on? Also has anyone actually done experiments on mammalian brain
tissues to determine the extent of cracking damage at LN2
temperatures? I know that autopsies on the bodies of post-suspension
neuroconversions have been done, but I haven't heard about tests on
actual brain tissue thus far, and that is, after all, what we are
preserving. If only to know how bad the problem for the existing
patients is, it would be useful to know precisely how bad the problem
is for brain tissue.
3. Lastly, it seems that people have dismissed using a working fluid
other than liquid nitrogen out of hand. It would seem, however, that
other fluids do exist with an appropriate boiling point and that they
are not considered primarily because of expense or toxicity. However,
it is unnecessary to actually expose the patients or employees to the
working fluid or to consume it -- one could simply use the liquid in a
closed recirculating system to exploit its boiling as a way of very
stably maintaining patients at a desired temperature. Patients could
be surrounded by dry gas or by a liquid with a suitably low freezing
point. Is this impractical in some way that I haven't thought of?
Perry Metzger
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